This invention is concerned with gaskets which are adapted when clamped between two bodies to seal with the gap between the bodies around a chamber or passage jointly defined by the bodies. The invention also relates to a method of sealing and two bodies including a gasket. Such a gasket may be used, for example, for sealing the gap between flanges at the ends of pipes.
Gaskets require to be resilient in order to achieve a seal. In some gaskets, the resilience is achieved by using inherently resilient material such as rubber or cork. In other gaskets, the resilience is achieved by utilising metal which resists being bent out of its initial shape. This invention is concerned with a gasket of the latter type which comprises a sealing member which forms a closed loop extending around a hole which corresponds to the chamber or passage and which offers resilient resistance. Such gaskets are often in the shape of an annular ring but may have other shapes. Accordingly, the term xe2x80x9cringxe2x80x9d is used herein to include a continuous band surrounding a hole of any shape.
Gaskets made of springy metal are known which have a sealing member which has a generally X-shaped transverse cross-section and comprises two arms which project inwardly of the hole, and two arms which project outwardly of the hole, the inwardly projecting arms being adapted to each resiliently engage one of the bodies to form a first seal around said hole, and the outwardly projecting arms being adapted to each resiliently engage one of the bodies to form a second seal around said hole. Examples of this type of gasket are described in GB 908,044, GB 1,540,465, GB 1,190,537 and 495,874. In these gaskets, the arms have parallel sides and, in some cases, rounded tips. Thus, the arms have substantially equal thickness from their junction with the remainder of the gasket to a point adjacent the tip. It is found in practice that the arms of such gaskets are prone to plastic deformation and/or cracking at their junction with the remainder of the gasket with a consequent loss of seal.
It is an object of the present invention to provide a gasket of the type described which overcomes at least some of the above disadvantages, especially at elevated temperatures and over extended time periods.
One aspect of the present invention provides a gasket adapted when clamped between two bodies to seal the gap between the bodies around a chamber or passage jointly defined by the bodies, the gasket comprising a sealing member which forms a closed loop extending around a hole which corresponds to the chamber or passage, the sealing member being formed from resilient metal, wherein the sealing member comprising two arms which project inwardly of the hole, the inwardly projecting arms being adapted to each resiliently engage one of the bodies to form a first seal around said hole, wherein each arm extends from a junction with the remainder of the gasket to a tip of the arm, and each arm has its greatest thickness at said junction and a lesser thickness away from the junction.
The sealing member may have a cross-section which is generally X-shaped in which two arms project outwardly of a hole with the outwardly projecting arms extending from a junction with the remainder of the gasket to a tip of the arm and with the outwardly projecting arms being adapted to each resiliently engage one of the bodies to form a second seal around the hole.
In a gasket according to the invention, it is found that the continuous reduction in thickness of each arm prevents the build-up of stresses thereby reducing the likelihood of plastic deformation or cracking. Of course, references herein to xe2x80x9cthicknessxe2x80x9d are intended to refer to the minimum thickness, ie the thickness of the arm at any point along the arm is considered to be the shortest distance measured from said point through the arm. Thus, said thickness is not necessarily measured in parallel directions at different points along said arm, because, for example, the arm may be curved.
In a gasket according to the invention, the thickness of each arm may decrease at a constant rate between said junction and said thinnest point. Alternatively, this rate may very. For example, the rate of thickness reduction of the arm may reduce as the thinnest point is approached.
In a gasket according to the invention, each arm may be bounded by a generally frusto-conical surface, which it presents to the body which it engages. Alternatively, this surface may be convex or concave. Each arm may also be bounded by a concave surface, ie the surface which faces away from the body engaged by the arm may be concave. In order to reduce the risk of plastic deformation or cracking at the junction, the sealing member, preferably, has curved surfaces which may be smooth between the junctions of the inwardly projecting arms. References herein to the shapes of surfaces of arms assume that the arms have not been deformed by the application of stress thereto. It is not necessary that the arms be bounded by simple geometric shapes, for example the bounding surfaces may undulate.
A sealing member according to the invention may be formed in one piece as an extrusion which has its ends joined together, ie the extrusion is formed into a loop and has its ends joined together, eg by welding, the weld then being dressed.
In alternative constructions, the sealing member is formed by forming a ring to the required transverse cross-section by machining or by a combination of machining and deformation. The ring can be cut from a sheet, formed from strip with the ends being welded together, cut from the end of a cylinder etc. For example, slots can be machined into the top and the bottom surfaces of the ring (which then has a cross-section in the shape of an xe2x80x9cHxe2x80x9d) and this machined ring can be bent to an X-cross section. The slots can alternatively be machined into the inside and outside surfaces of the ring.
A gasket according to the invention may also comprise layers of deformable material secured to said arms at least in the areas thereof which engage said bodies. This deformable material, which may, for example, be expanded graphite, mica, expanded vermiculite, soft metal or PTFE, is not intended to provide the major sealing force but is intended to fill small fissures or cracks in the body or the arm to thereby improve the seal. The arms may be provided with ridges running circumferentially of the sealing member and the deformable material may cover these ridges. The ridges have the functions of reducing the possibility that the deformable material will be extruded from the seal and of providing local stress concentration.
In order to prevent the sealing member from being crushed to such an extent that resilience is lost, the gasket may also comprise a compression-limiting stop. The stop may be provided by a projection from a central region of the sealing member. Alternatively, a compression-limiting stop may be secured to the sealing member. That stop may be at a central region between the first and second seals. Compression limiting stops may be welded or otherwise secured to both the top and the bottom of the sealing member. It is also possible to position a compression limiting stop between the inwardly facing arms or between the outwardly facing arms, ie such a stop may be in the form of a ring. Compression stops may also be provided by rings positioned inwardly and/or outwardly of the gasket.
In order to provide different levels of sealing with a single gasket, the inwardly projecting arms of a gasket according to the invention may have a different spacing and stiffness to the outwardly projecting arms. In this case, the further spaced arms can provide a seal at a first, lighter, clamping stress and, the closer spaced arms can provide a seal at a second, higher, clamping stress.
The arms may be arranged to yield from a location away from the junction in a direction towards the junction as the pressure on the gasket is increased.
According to a further aspect of the present invention a method of sealing the gap defined around a chamber or passage jointly defined by two bodies with a gasket comprises clamping the gasket between the two bodies, the gasket comprising a sealing member which forms a closed loop extending around the hole which corresponds to the chamber or passage, the sealing member being formed from resilient metal, comprising two arms which project inwardly of the hole, the inwardly projecting arms each resiliently engaging one of the bodies to form a first seal around said hole, wherein each arm extends from a junction with the remainder of the gasket to a tip of the arm, and each arm has its greatest thickness at said junction and a lesser thickness away from this junction, the method further comprising arranging for the part of the arms that engage with the bodies to move progressively towards the junction as the gasket pressure increases.
The gasket may comprise two arms which project outwardly of the hole which each resiliently engage one of the bodies to form a second seal around the hole with each outwardly projecting arm extending from a junction with the remainder of the gasket to a tip of the arm and with each outwardly projecting arm having its greatest thickness at the junction and a lesser thickness away from this junction, the method comprising arranging for the part of the outwardly projecting arms that engage with the bodies to move progressively towards the junction as the pressure increases.
The rate that the part of the arms that engage with the bodies moves towards the junction as the pressure increases may decrease, given a.constant rate of increase of pressure.
The method may comprise the arms yielding as the part of the arms that engage with the bodies moves towards the junction.
The gasket may include layers of deformable material secured to the arms at least in the areas that engage the bodies and the method may comprise the deformable material moving away from the free end of at least one arm as the pressure increases. The method may comprise the deformable material on two arms that engage the same body moving away from the ends of those arms towards each other. In this way the deformable material is concentrated in the centre and pressurised to produce an increasingly efficient area of sealing.
The present invention also includes two bodies defining a chamber or passage incorporated a gasket as herein referred to.